Method of making abrasive articles



UNITED STATES PATENT OFFICE v METHOD OF MAKING ABRASIVE ARTICLES Raymond C. Benner and Romie L. Melton, Niagara Falls, N. Y., assignors, by mcsne assignments, to The Carborundum Company, Niagara Falls, N. Y., a corporation of Delaware No Drawing. Application October 19, 1936,

Serial No. 106,374

Claims. (C1. 51-278) This invention relates to improved abrasive arbacking. Our invention therefore has the adticles and methods of manufacturing the same. vantages inherent in the use of processes for ap- The invention is particularly concerned with plying water-insoluble plastic binding agents in methods of making coated abrasive articles the form of aqueous suspensions, such as the 5 wherein the adhesive is applied in the form of an elimination of the costly and more or less dan- 5 aqueous suspension. gerous organic solvents heretofore employed.

This application is a continuation in part of Our invention also makes it possible to utilize in our copending application Serial No. 735,825, the production of abrasive coated products bindfiled July 18, 1934. ing agents which are in a condition where they The most common adhesive for coated abraare poorly adhesive to abrasive grains and to 10 sive articles is glue and glue-bonded sandpaper the backing to which the grains are to be atis very old in the art. With the advent of imtached. Entirely additional to these practical proved forms of synthetic materials, which are considerations of manufacturing processes, the broadly classed as plastics and include such products obtained by the method of our inven- 5 products as certain kinds of synthetic resins and tion have been found to be particularly eificient l6 cellulose esters, it has been found that coated in use.

abrasive products which are especially valuable In accordance with our invention, we suspend for particular purposes can be made employing the normally-solid plastic binding material in these new plastic materials. However, the prodwater, coat the backing material with the susucts of this type have the serious disadvantage pension and with abrasive grains, and then treat from a practical manufacturing standpoint that the thus coated article to develop adhesiveness they are soluble only in special kinds of organic in the binding material so that it will adhere to solvents which are relatively expensive and some both the grains and the backing and will weld of which are highly inflammable. Because of this into a continuous body attaching the grains to cost it is necessary to employrelatively costly the backing. The treatment which we employ to equipment for recovery of the solvent and bedevelop this adhesiveness of the binding material cause of the flammability special precautions depends upon the nature .of the binding material are necessary to prevent explosions. Conseand the composition of the aqueous suspension quently, the use of these new adhesives has been thereof.

limited. One way of overcoming these difficul- One method which we have successfully em- 30 ties is to liquefy the plastic materials by susployed consists in incorporating with the bindpending them in water as in the form, of colloidal ing material a. substance which, when the water dispersions. is removed from the film of dispersion which has However, it has been found that when colbeen coated onto the backing, will soften the parloidal dispersions of plastic materials are subticles of binding material and develop adhesive- 35 stituted for glue or for solutions of the mateness in them.' An example of this modification rials, inferior products are obtained if the ordiof our invention consists in the inclusion in the nary methods of making the articles are embinding material of a water-insoluble solvent for ployed. Articles made with colloidal dispersions the binder which is of sufficiently high boiling 40 of plastic materials which are highly satisfactory point so that it will not be evaporated when the 40 when applied as solutions are poorly eflicient and 4 water is removed but will remain on the backing tend to shed the abrasive grains. to develop adhesiveness of the binder. For ex- We have discovered amethod by which articles ample, we have been able to plastify a binder can be made from aqueous suspensions or colconsisting principally of vinyl resin by including loidal dispersions of plastic materials which are ethylene dichloride with the resin prior to dis- 45 equally satisfactory as articles made from solupersing the resin in water. tions of the materials. Our discovery leads us Another method by which we have been able to believe that the difficulties heretofore experito plastify binding materials consists in disenced with aqueous suspensions is caused by the solving in the water which is to form the con- 60 poor adhesion of the plastic materials as they tinuous suspending phase of the dispersion, a-

' are deposited from the suspension. "The method relatively small quantity of water-soluble, highcomprises, as an essential step, a. treatment to boiling solvent for the binder. For example, we make the plastic, or more correctly the plastihave suspended a pulverized A stage phenolaldeflable, binding material sticky enough to behyde product in water containing a small quancome strongly attached, to the grains and to the tity of furfural. Furfural is a solvent for the 55 phenolic resin and when the water had been evaporated there was sufficient furfural remaining to make the particles of solid resin sufliciently sticky and tacky so that they adhered to the backing and to the abrasive grains. A modification of this method consisted in wetting the abrasive grains with a small quantity of furfural so as to supply additional solvent and further promote adhesion of the pulverized resin to the grains. Adhesion of the resin to the backing was also promoted by moistening the surface of the backing which was to be coated with the dispersion with furfural. When the water was removed from the dispersion, the furfural dissolved the surface of the resin particles immediately in contact with the backing and increased adhesion of the resin to the backing as in the case of furfural coated grains where adhesion to the grains was improved. Aqueous suspensions of solid resins of this character deposit a film of a solid resin which is normally non-tacky and very poorly adhesive.

Still another method which we have used to plastify and render binding materials adhesive consists in forming colloidal dispersions including a dispersing agent for the binder which becomes adhesive when the water is removed from the dispersion and thereby causes adhesion of the deposited particles to the backing-and to the grains. Examples of such adhesives, which may be spoken of as temporary adhesives because they function primarily to assist in adhesion of the grains to the backing in the freshly coated article, comprise such products as glue, polyvinyl alcohol and methyl cellulose. In our invention these materials perform the dual function of suspending the particles of solid binding material in water and subsequently acting as the temporary adhesive for holding the constituents of the article together until the binding material itself is subsequently rendered plastic and made to attach itself to the grains and to the backing and to weld together.

The methods of coating which we have used are those commonly employed in the production of coated abrasives. For example, a web ofbacking material can be fed through a sandpapermaking machine where a film of the suspension or dispersion is spread onto the backing by a roll which rotates partially immersed in a vat of the dispersion. The adhesive-coated web is theri fed under a hopper where abrasive grains are dropped onto the coated surface, and the thuscoated article is caused to travel along into chambers where the water can be removed and the adhesiveness of the binder, can be developed. Alternatively, the dispersions may be sprayed onto a backing which may be either in the form of a web or in the form of individual articles such as disc-shaped backings.

Following the removal of the moisture and the treatment to develop adhesiveness, thearticle may be subjected to heat treatment to make the particles of binding material plastic and cause the welding together of the individual particles deposited from the dispersions. Alternatively, this adhesiveness may be developedby applying a coating of solvent to the article so as to dissolve the outer surface of the binding material and cause welding, followed by treatment to evaporate the solvent which has been thus applied. In the case of heat-hardenable binders, such as heat-reactive phenolic condensation products, additional treatment to harden up the, resin to the infusible insoluble condition may be applied as by heating.

The adhesive may all be applied in one step before the abrasive grains are distributed onto the adhesive-coated backing but it is usually more satisfactory to add a second coating of adhesive after the abrasive grains have been applied. The treatments to remove water and to promote'adhesion may be carried out either before or after the addition of the second or sizing coating of adhesive according to the steps commonly employed in the manufacture of abrasive ,coated products. The second or sizing coating of adhesive may be a dispersion or, for that matter, the adhesive may be applied in various forms as by dusting on a powdered adhesive and the second adhesive may or may not be of the same composition as the first or making coat.

As has been indicated, our invention has a number of advantages. It provides a method for using water-insoluble plastic materials in making abrasive coated products which is commercially practical because it dispenses with the organic solvents heretofore employed or, at least, reduces to a minimum the amount of solvent which must be used. The aqueous suspensions are non-tacky and it is easy to distribute them in coatings of uniform thickness. Furthermore, they are of relatively high concentration as contrasted to solutions of many of these materials which are so viscous that it is necessary to use a comparatively dilute solution in order to be able to distribute the solutions on the backings.

It will be understood that various modifying agents can be incorporated in the binding materials to develop degrees of flexibility and toughness as such modifications are well understood in the art of preparing plastic binders. within the scope of our invention to employ other practices common in the production of abrasive coated products such as inclusion of inert fillers with the binding material; as, for example, by utilizing an inorganic dispersing agent such as bentoniteor other clay which blends with the organic plastic binding material when the article is treated to weld the individual particles of the binder together. I

Other modifications and embodiments of our invention may be practised without departing from the spirit of the invention as defined by the appended claims.

We claim:

1. In the manufacture of abrasive coated products, the steps which comprise preparing an aqueous suspension of a water-insoluble binder which is normally poorly adhesive but adapted to be made adhesive by wetting with a solvent, coating a backing with abrasive grains and with the said suspension, removing the water from the suspension, and treating the article with a solventto cause the binder to adhere to the grains and to the backing.

2. In the manufacture of abrasive coated products the steps which comprise preparing an aqueous suspension of a water-insoluble binder which is normally poorly adhesive but adapted to be made adhesive by wetting with a solvent, preliminarily wetting a backing with a solvent for the grains and with the said suspension, and removing water from the suspension.

3. In the manufacture of abrasive coated products the steps which comprise preparing an aque ous suspension of a normally solid phenolic resin in water, coating the backing with abrasive grains It is also binder, coating the wetted backing with abrasive and with the said suspension, removing the water from the suspension, and treating the article with a solvent for the resin to make the resin adhesive.

4. In the manufacture of abrasive coated products, the steps which comprises preparing a suspension of a water-insoluble bond in water, which bond is normally poorly adhesive, coating a backing with said suspension and abrasive grains, removing the water' from the suspension, and. rendering the bond adhesive by wetting with a solvent.

\ 5. In the manufacture of abrasive coated products, the steps which comprise suspending a water-insoluble bond in a liquid mixture of water and a substance which is a. solvent for the bond in the absence of water, coating a backing with said suspension and abrasive grains, and removing the water from said suspension whereby the adhesive is caused to adhere to the backing and grain.

RAYMOND C. BENNER.

ROMIE L. MELTON. 

